CAMRT Radiography Practice Exam

The late arterial phase is critical in detecting tumor nodules during a triphasic CT examination of the liver because it provides images at a time when the vascular supply to the tumors, often arising from the hepatic artery, enhances relative to the surrounding liver parenchyma. This phase captures the optimal contrast enhancement of hypervascular lesions, which are common in hepatocellular carcinoma and certain metastases, allowing for improved visualization and differentiation from the surrounding liver tissue.

In the late venous phase, the contrast enhancement shifts as the hepatic veins and inferior vena cava become more prominent, potentially obscuring smaller arterial tumors. The venous phase provides less distinction between normal and tumor tissue for hypervascular lesions, making it less effective for initial tumor detection. The early arterial phase, while showing initial enhancement, does not offer the same level of contrast between tumors and liver tissue as the late arterial phase, as tumors may not yet fully enhance during this time. Thus, the timing of the late arterial phase is optimal for identifying tumor nodules.